OBJECT:

Prompt diagnosis of shunt malfunction is critical in preventing neurological morbidity and death in individuals with hydrocephalus;
however, diagnostic methods for this condition remain limited. For
several decades, investigators have sought a long-term, implantable
intracranial pressure (ICP) monitor to assist in the diagnosis of shunt
malfunction, but efforts have been impeded by device complexity, marked
measurement drift, and limited instrumentation lifespan. In the current
report, the authors introduce an entirely novel, simple, compressible
gas design that addresses each of these problems.

METHODS:

The
device described herein, termed the "baric probe," consists of a
subdural fluid bladder and multichannel indicator that monitors the
position of an air-fluid interface (AFI). A handheld ultrasound probe is
used to interrogate the baric probe in vivo, permitting noninvasive ICP
determination. To assess the function of device prototypes, ex vivo
experiments were conducted using a water column, and short- and
long-term in vivo experiments were performed using a porcine model with
concurrent measurements of ICP via a fiberoptic monitor.

RESULTS:

Following
a toe region of approximately 2 cm H(2)O, the baric probe's AFI
demonstrated a predictable linear relationship to ICP in both ex vivo
and in vivo models. After a 2-week implantation of the device, this
linear relationship remained robust and reproducible. Further, changes
in ICP were observed with the baric probe, on average, 3 seconds in
advance of the fiberoptic ICP monitor reading.

CONCLUSIONS:

The
authors demonstrate "proof-of-concept" and feasibility for the baric
probe, a long-term implantable ICP monitor designed to facilitate the
prompt and accurate diagnosis of shunt
malfunction. The baric probe showed a consistent linear relationship
between ICP and the device's AFI in ex vivo and short- and long-term in
vivo models. With a low per-unit cost, a reduced need for radiography or
CT, and an indicator that can be read with a handheld ultrasound probe
that interfaces with any smart phone, the baric probe promises to
simplify the care of patients with shunt-treated hydrocephalus throughout both the developed and the developing world.